1. Field of the Invention
The present invention relates to an optical recording/reproducing apparatus, and especially to a signal deviation measuring system and method applied to an optical recording/reproducing apparatus.
2. Prior Art
Refer to FIG. 1, which is a diagram showing a conventional optical pickup head in a state of reading data. The optical recording/reproducing apparatus 4 uses the pickup head 2 to read the data. The pickup head includes a lens set 8 and a light source 6 for emitting a light beam 16. The light beam 16 goes through the lens set 8 and then focuses on a surface of an optical recording medium 10 such as a compact disk. As shown, the light beam 16 reflects back from the optical recording medium 10 and then projects onto a photodetector 12 located in the pickup head 2. The photodetector 12 identifies the projected light beam 16 and transforms it into relevant electric signals that realize the data recorded by the surface of the optical recording medium 10.
Refer to FIG. 2, which is a diagram showing a main beam 16a and a sub-light beam 16b of the light beam 16 of FIG. 1. In the optical recording technique, data is stamped on the surface of the optical recording medium 10 as a spiral track 14. In order to read the accurate position in the spiral track 14, the pickup head 2 can correct the beam position by analyzing a tracking error signal while in tracking the spiral track 14.
In a high-capacity optical recording/reproducing apparatus, such as a DVD+R/RW or a DVD-R/RW, a differential push pull (DPP) method is used to calculate a tracking error signal. As stated above that the light beam 16 emitted from the light source 6 includes the main beam 16a and the sub-beam 16b, after the light beam 16 is reflected from the optical recording medium 10, the main beam 16a and the sub-beam 16b would represent as a main beam push pull (MPP) and a sub-beam push pull (SPP). The MPP signal and the SPP signal are combined as the differential push pull (DPP), and the pickup head 2 uses the DPP signal to track the spiral track 14 and correct the beam position.
The electric signal mentioned above can be transported to the IC board of the optical recording/reproducing apparatus 4. Generally speaking, the MPP signal and the SPP signal can be acquired from the IC board of the optical recording/reproducing apparatus 4 by using a data acquisition card (DAQ card). The MPP signal and the SPP signal being acquired can be realized as a sine wave (maybe represented by sin(ωt)). However, the optical recording/reproducing apparatus 4 always has some built-in errors, for example the manufacturing tolerances of the pickup head 2 or optical errors generated from inaccurate mounting of the lens set 8. All these errors would cause the light beam center and its moving direction to shift away along a radial direction of the optical recording medium 10. Thus, the built-in errors would weaken the DPP signal to an unrecognizable degree. Definitely, wrong realization upon the data would be inevitable.